The present invention relates to a method for the determination of the content of one or more gas components in the respiratory gas of a patient on the basis of samples picked up from a plurality of respiratory cycles, several successive samples being accommodated in the same sample chamber prior to the actual determination. An apparatus used in such determination comprises a tube to be placed in the windpipe and provided with a means detecting the reversal of a respiratory gas flow and/or or of a respiration device. The apparatus also includes a sampling tube provided with a means measuring the content, of a gas component, a valve and a pump or a reduced pressure chamber and a control means controlling the operation of such elements. This method is particularly useful for finding out the content of a gas component or gas components in the exhalation gases of small children, such as newborn babies, since small children have a high respiration frequency and a small respiration volume. The most notable gas component to be measured is carbon dioxide.
Measurements of the carbon dioxide content in the exhalation gases of a patient have been effected by continuously pumping a sample from the exhalation gases to a CO.sub.2 -sensor. In adults, this method is capable of providing reasonably good results over the entire breathing cycle but in small children, reliable measurement of the final CO.sub.2 -content in exhalation gases has not been possible due to a high respiratory frequency and a small respiratory volume. The small respiratory volume provides a very small sample that must be carried along a lengthy tube to a CO.sub.2 -sensor. Inevitably, other gases along with exhalation gases will enter the tube, the mixing and dead space having a substantial effect on the measurement. Thus, the test results become distorted and provide an incorrect indication of the carbon dioxide level. Therefore, this method cannot be applied to small children.
The determination of the final CO.sub.2 -content in exhalation gases is possible by using a miniaturized sensor which is placed immediately adjacent to the head of a patient. However, dead space is a problem also in this method. Another drawback is the high cost of this method and it is also inconvenient to apply in case of small children.
An object of this invention is to eliminate the above drawbacks. The object is to provide a reliable determination method for one or a plurality of gas components in the respiratory or alveolar gas of a patient and particularly infant patients, whereby a small respiratory volume and a high respiratory frequency are not a problem. Another object is to provide a method which is easy to operate, pleasant to a patient and economical in terms of equipment costs.
The characterizing features of the invention are set forth in the annexed claims.